Java operator precedence can cause unexpected output

My Java program needed to determine whether a particular variable was null. I wasn't getting the expected results, so I added a System.out.println call to print some diagnostic output to the console. The diagnostic output wasn't what I expected, either. It turned out to have to do with operator precedence in Java. Here's some example code that illustrates the problem:

public class Example {
 public static void main(String[] args) {
  Integer n = 1;
  System.out.println("Is n null? " + n == null);
 }
}

I expected the output to be: Is n null? false. Instead, it was just the single word false. Here's why:

The additive operator + has higher precedence than the equality operator ==. So Java was evaluating the string concatenation

"Is n null? " + n

and then comparing the result to null. The result of that comparison was the boolean value false, which is what was displayed. This was easily fixed with the addition of a couple of parentheses:

System.out.println("Is n null? " + (n == null));

Interestingly, if I'd been comparing n to some integer rather than to null, the compiler would have caught the problem for me. This code

public class Example {
 public static void main(String[] args) {
  Integer n = 1;
  System.out.println("Is n one? " + n == 1);
 }
}

causes a compile-time error, Incompatible operand types String and int.

The moral of the story is, whatever language you're programming in, be aware of operator precedence!